document.write( "Question 1170709: Hi, I need help
\n" ); document.write( "A cube is expanding in such a way that its sides are changing at a rate of
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Algebra.Com's Answer #795598 by ikleyn(52788) $\"\"$ $\"About$

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document.write( "The surface area of a cube is  S(a) = 4a^2,  where \"a\" is the edge size.\r\n" );
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document.write( "We have edge size depending on time  a = a(t);  therefore, the rate of the surface area change is the derivative\r\n" );
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document.write( "    S'(t)  =  4*2*a(t)*a'(t)  =  8*a(t)*a'(t)  .     (1)\r\n" );
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document.write( "The value a'(t) is given : it is  a'(t) = 2 cm/s.\r\n" );
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document.write( "The value of \"a\" is a= 5, when the volume is 125 cm^3.\r\n" );
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document.write( "Therefore,  the rate of the surface area change is, according the formula (1), \r\n" );
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document.write( "    S'(t) = 8*5*2 = 80 .     ANSWER\r\n" );
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\n" ); document.write( "\n" ); document.write( "Solved, answered and explained. And completed.\r
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